Method for manufacturing semiconductor device

ABSTRACT

A method for manufacturing a semiconductor device includes forming, on first and second impurity layers on a termination region side, an insulating layer, forming a first metal film and a second metal film in this order on the insulating layer and a drift layer, performing dry etching on the first and second metal films all together so that a position of a first end of a metallized layer, which is a remaining part of the first metal film, in the interface region on the termination region side and a position of a second end of an electrode, which is a remaining part of the second metal film, in the interface region on the terminal region side are the same in plan view. The first and second ends are closer to the active region than an end of the second impurity layer on the termination region side in plan view.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No. 16/845,716 filed Apr. 10, 2020, which claims priority to and the benefit of Japanese Patent Application No. 2019-110328 filed Jun. 13, 2019, the entire contents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a semiconductor device and a method for manufacturing a semiconductor device.

Description of the Background Art

A diode including a metallized layer functioning as a Schottky metal and an electrode provided thereon has been proposed. For example, Japanese Patent Application Laid-Open No. 2015-211179 proposes a technique for patterning a metallized layer and an electrode all together by wet etching.

However, in a case where wet etching is performed as described in Japanese Patent Application Laid-Open No. 2015-211179, the following problems occur. When etching selectivity of the metallized layer with respect to the electrode is large, an end of the metallized layer is etched to an inner side of the metallized layer more than an end of the electrode so that a cave-like shape is created. Meanwhile, when the etching selectivity of the metallized layer with respect to the electrode is small, a whisker-like residue is generated in the metallized layer.

As described above, according to the technique of Japanese Patent Application Laid-Open No. 2015-211179, the metallized layer may not be appropriately patterned. This results in variations in performance such as electrical characteristics among manufactured semiconductor devices, leading to a decrease in reproducibility of the semiconductor devices and eventually to a decrease in reliability of the semiconductor devices. The above problems become more apparent especially in a case where a thickness of the metallized layer is on the order of submicrons and a thickness of the electrode is several microns or more, that is, in a case where the thickness of the electrode is several tens of times the thickness of the metallized layer.

SUMMARY

The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of improving the reliability of a semiconductor device.

A method for manufacturing a semiconductor device includes preparing a buffer layer having a first conductivity type. On the buffer layer, form a drift layer in which an active region, an interface region that surrounds the active region, and a termination region that surrounds the interface region are defined, the drift layer having the first conductivity type. In a surface of the drift layer in the interface region, form a first impurity layer, the first impurity layer having a second conductivity type. In a surface of the first impurity layer, form a second impurity layer that has a side and a bottom covered with the first impurity layer and that has a higher impurity concentration than the first impurity layer, the second impurity layer having the second conductivity type. On the first impurity layer and the second impurity layer on a termination region side, form an insulating layer from which the first impurity layer and the second impurity layer on an active region side are exposed. Form a first metal film and a second metal film in this order on the insulating layer and the drift layer, and perform dry etching on the first metal film and the second metal film all together so that a position of a first end of a metallized layer, which is a remaining part of the first metal film, in the interface region on the termination region side and a position of a second end of an electrode, which is a remaining part of the second metal film, in the interface region on the terminal region side are the same in plan view. The first end and the second end are closer to the active region than an end of the second impurity layer on the termination region side in plan view.

The reliability of the semiconductor device can be improved.

These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a configuration of a semiconductor device according to a first preferred embodiment;

FIG. 2 is a cross-sectional view illustrating a configuration of the semiconductor device according to the first preferred embodiment;

FIG. 3 is a cross-sectional view illustrating a configuration of a related semiconductor device; and

FIGS. 4 to 9 are cross-sectional views each illustrating a step for manufacturing the semiconductor device according to the first preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Preferred Embodiment

Hereinafter, a configuration in which a first conductivity type is n-type and a second conductivity type is p-type will be described as an example. However, this configuration is not restrictive, and the first conductivity type may be p-type and the second conductivity type may be n-type.

FIG. 1 is a plan view illustrating a configuration of a semiconductor device according to the first preferred embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line A-A′ of FIG. 1. As illustrated in FIG. 1, in the semiconductor device according to the first preferred embodiment, an active region 2 a, an interface region 2 b surrounding the active region 2 a, and a termination region 2 c surrounding the interface region 2 b are defined.

The semiconductor device of FIG. 2 includes a buffer layer 1, a drift layer 2, p injection layers 3 a, 3 b, 3 c, p⁺ injection layers 4 a and 4 b, an oxide film 5, and a metallized layer 6 functioning as a Schottky metal, an electrode 7, a coating sealing material 8, and a back surface electrode 9.

The conductivity type of the buffer layer 1 is n⁺, and an n-type impurity concentration of the buffer layer 1 is relatively high. In the following description, it is assumed that the buffer layer 1 is a semiconductor substrate. Note, however, that the buffer layer 1 is not limited to this, and may be, for example, an epitaxial growth layer.

The drift layer 2 is provided on the buffer layer 1. The conductivity type of the drift layer 2 is and an n-type impurity concentration of the drift layer 2 is relatively low. A total thickness of the buffer layer 1 and the drift layer 2 is, for example, 100 μm. In the first preferred embodiment, it is assumed that a material of the buffer layer 1 and the drift layer 2 is silicon carbide (SiC). Note, however, that the material of the buffer layer 1 and the drift layer 2 is not limited to this and can be any of other wide band gap semiconductors such as gallium nitride (GaN) and diamond or silicon (Si).

In the drift layer 2, the active region 2 a, the interface region 2 b, and the termination region 2 c described above are defined. In the active region 2 a, for example, at least one of a metal oxide semiconductor field effect transistor (MOSFET), a Schottky barrier diode (SBD), a junction barrier Schottky (JBS), a merged pin Schottky (MPS) diode, and an insulated gate bipolar transistor (IGBT) is provided.

The p injection layers 3 a, 3 b, and 3 c form a structure for alleviating electric field concentration at an end of the Schottky electrode so that a required withstand voltage is stably ensured in the semiconductor device. The p injection layer 3 a, which is a first impurity layer, is provided in a surface of the drift layer 2 in the interface region 2 b and forms a guard ring. The conductivity type of the p injection layer 3 a is p. A position of an end of the p injection layer 3 a on the active region 2 a side corresponds to a position of a boundary between the active region 2 a and the interface region 2 b, and a position of an end of the p injection layer 3 a on the termination region 2 c side corresponds to a position of a boundary between the interface region 2 b and the termination region 2 c. Note that “correspond” as used herein means “same” or “almost same”.

The p injection layer 3 b is provided in the surface of the drift layer 2 in the active region 2 a and forms a JBS. The p injection layer 3 c is provided in the surface of the drift layer 2 in the termination region 2 c and forms a junction termination extension (JTE) or a field limiting ring (FLR).

The p⁺ injection layers 4 a and 4 b are provided in order to further stably secure a required withstand voltage in the semiconductor device. The p⁺ injection layer 4 a, which is a second impurity layer, is provided in the surface of the p injection layer 3 a, and a side and a bottom of the p⁺ injection layer 4 a are covered with the p injection layer 3 a. The conductivity type of the p⁺ injection layer 4 a is p⁺, and an impurity concentration of the p⁺ injection layer 4 a is higher than an impurity concentration of the p injection layer 3 a. The p⁺ injection layer 4 a forms a guard ring similarly to the p injection layer 3 a.

The p⁺ injection layer 4 b is disposed in the surface of the p injection layer 3 b, and a side and a bottom of the p⁺ injection layer 4 b are covered with the p injection layer 3 b. The conductivity type of the p⁺ injection layer 4 b is p⁺, and an impurity concentration of the p⁺ injection layer 4 b is higher than an impurity concentration of the p injection layer 3 b. The p⁺ injection layer 4 b forms a JBS similarly to the p injection layer 3 b.

The oxide film 5, which is an insulating layer, is provided on the p injection layer 3 a and the p⁺ injection layer 4 a on the termination region 2 c side while exposing the p injection layer 3 a and the p⁺ injection layer 4 a on the active region 2 a side. In the first preferred embodiment, the oxide film 5 in the interface region 2 b extends so as to extend beyond a position of p injection layer 3 c in termination region 2 c. A material of the oxide film 5 is, for example, silicon dioxide (SiO₂).

The metallized layer 6 is provided on the p injection layer 3 a and p⁺ injection layer 4 a exposed from the oxide film 5 and on the oxide film 5. In the first preferred embodiment, the metallized layer 6 is provided not only in the interface region 2 b but also in the active region 2 a.

In the following description, it is assumed that a material of the metallized layer 6 is titanium (Ti). Note, however, that the material of the metallized layer 6 is not limited to this, and may be a metal material such as molybdenum (Mo) or tungsten (W). According to such a configuration, a good Schottky junction can be obtained. A work function of the metallized layer 6 and a pinning effect with SiC vary depending on the metal material of the metallized layer 6, and a forward barrier height φB obtained as, for example, diode characteristics also varies depending on the metal material of the metallized layer 6 accordingly. Therefore, the metal material of the metallized layer 6 may be selected according to the specifications of the semiconductor device. In a case where a dry thermal oxide film is formed as a protective film immediately before forming the metallized layer 6 on the drift layer 2 having a Schottky interface is stabilized. This can improve uniformity of the barrier height and reduce a reverse leakage current.

The electrode 7 is provided on the metallized layer 6 as a metal pad. A material of the electrode 7 is, for example, aluminum (Al) or AlSi. In the first preferred embodiment, a thickness of the metallized layer 6 is, for example, approximately 200 nm, whereas a thickness of the electrode 7 is, for example, approximately several μm in consideration of wire bonding in a later step.

The coating sealing material 8 covers at least part of the oxide film 5, a first end 61 of the metallized layer 6 on the termination region 2 c side, and the electrode 7 in the interface region 2 b. A material of the coating sealing material 8 is, for example, polyimide.

The back surface electrode 9 is provided on a back surface of the buffer layer 1 opposite to a surface on which the drift layer 2 is provided.

In the first preferred embodiment, according to the above configuration, a position of the first end 61 of the metallized layer 6 on the termination region 2 c side and a position of a second end 71 of the electrode 7 on the termination region 2 c side almost match each other in plan view. That is, the first end 61 of the metallized layer 6 and the second end 71 of the electrode 7 are flush with each other. In the first preferred embodiment, the first end 61 and the second end 71 are located between an end of the p⁺ injection layer 4 a on the active region 2 a side and an end of the p⁺ injection layer 4 a on the termination region 2 c side in plan view.

As described above, in the first preferred embodiment, the position of the first end 61 of the metallized layer 6 and the position of the second end 71 of the electrode 7 are the same in plan view, and there is substantially no gouging or residue at the first end 61 of the metallized layer 6. This can suppress variations in performance such as electric characteristics of the semiconductor device, leading to improvement of reproducibility of the semiconductor device and eventually to improvement of reliability of the semiconductor device.

The following describes a semiconductor device (hereinafter referred to as a “related semiconductor device”) related to the first preferred embodiment configured to suppress the influence of gouging or residue in the first end 61 of the metallized layer 6. FIG. 3 is a cross-sectional view illustrating a configuration of the related semiconductor device. In the configuration of FIG. 3, the electrode 7 covers the first end 61 of the metallized layer 6. According to the related semiconductor device configured as described above, it is possible to suppress the influence of gouging or residue in the first end 61 of the metallized layer 6. However, since it is necessary to perform patterning on each of the metallized layer 6 and the electrode 7, there is a new problem that a manufacturing cost is relatively high.

As a method for suppressing the influence of gouging and residue of the first end 61 of the metallized layer 6, a lift-off method may be used for patterning the metallized layer 6 and the electrode 7, separately from the related semiconductor device. In this lift-off method, a metal film is formed on an entire surface of a photoresist selectively exposed in advance, and an ultrasonic wave or the like is applied thereto in an organic solvent such as acetone which dissolves the photoresist. As a result, only a part of the metal film formed on the dissolved photoresist is removed, and the other part of the metal film remains. That is, the metal film is patterned. Use of such a lift-off method can pattern a multilayer metal electrode such as the metallized layer 6 and the electrode 7 all together.

However, patterning using the lift-off method still tends to cause problems such as generation of a residue. Although techniques such as a jet lift-off method have been developed, such techniques are often unsuitable for mass production. In particular, when the thickness of the electrode 7 is several μm or more, it becomes difficult to dissolve the photoresist with acetone or the like.

On the other hand, according to the method for manufacturing a semiconductor device according to the first preferred embodiment described below, it is possible to suppress gouging or residue at the first end 61 of the metallized layer 6.

<Manufacturing Method>

FIGS. 4 to 9 are cross-sectional views illustrating a method for manufacturing a semiconductor device according to the first preferred embodiment. For patterning described below, for example, a photomechanical process and an etching process are appropriately used.

First, for example, an n⁺ type semiconductor substrate made of 4H—SiC having an off angle of 8 degrees on the (0001) plane is prepared. Resistivity of this semiconductor substrate is, for example, approximately 0.02 Ω·cm. Since the semiconductor substrate serves as the buffer layer 1 when the semiconductor device is completed, the semiconductor substrate and the buffer layer 1 will be described below without distinction.

As illustrated in FIG. 4, the drift layer 2 is formed on the buffer layer 1 by epitaxial growth. An impurity concentration of the drift layer 2 is, for example, approximately 5×10¹⁵/cm³. The drift layer 2 is formed to have a thickness of, for example, approximately 5 μm to 30 μm so that a withstand voltage of the drift layer 2 becomes a desired withstand voltage of, for example, 600 V to 3300 V.

Then, as illustrated in FIG. 4, a patterned etching mask (not illustrated) is formed on the drift layer 2, and the p injection layers 3 a, 3 b, and 3 c are formed by injecting, for example, Al ions into the surface of the drift layer 2 exposed from the etching mask.

Next, as illustrated in FIG. 5, a patterned etching mask 11 such as SiO₂ is formed on the drift layer 2, and the p⁺ injection layers 4 a and 4 b are formed, for example, by injecting Al ions into surfaces of the p injection layers 3 a and 3 b exposed from the etching mask 11. Then, the p injection layers 3 a, 3 b, and 3 c and the p⁺ injection layers 4 a and 4 b are activated and recrystallized by high-temperature annealing at approximately 1600° C. to 1700° C.

Then, as illustrated in FIG. 6, the oxide film 5 patterned so as to expose the p injection layer 3 a and the p⁺ injection layer 4 a on the active region 2 a side is formed on the p injection layer 3 a and the p⁺ injection layer 4 a on the termination region 2 c side.

Then, as illustrated in FIG. 7, a first metal film 6 a having a thickness of, for example, approximately 200 nm and made of Ti is formed on an entire upper surface of the structure formed in the previous steps, that is, on the oxide film 5 and the drift layer 2 by a sputter deposition method.

Next, as illustrated in FIG. 8, a second metal film 7 a having a thickness of, for example, approximately several μm and made of Al or AlSi is formed on an entire upper surface of the structure formed in the previous steps, that is, on the first metal film 6 a by a sputter deposition method.

Then, as illustrated in FIG. 9, the first metal film 6 a and the second metal film 7 a are subjected to dry etching all together, so that a position of the first end 61 of the metallized layer 6, which is a remaining part of the first metal film 6 a, and a position of the second end 71 of the electrode 7, which is a remaining part of the second metal film 7 a, are made the same in plan view. In the first preferred embodiment, etching gas for this dry etching includes BCl₃ and Cl₂. This enables highly controllable and uniform etching.

In a case where AlSi is used as a material of the second metal film 7 a, which will be the electrode 7, a smaller etching rate of Si, which is one of constituent atoms, may result in that an Si portion becomes an etching mask and may result in that Al, which is the other constituent atom immediately below Si, becomes a columnar residue. However, by adjusting conditions such as a gas flow ratio of BCl₃/Cl₂, a vacuum pressure, power, and temperature, etching rates of Al and Si can be optimized, and the residue can be reduced accordingly. In addition, since an etching time of the relatively thick second metal film 7 a is not long, an overetching amount of the oxide film 5 and the drift layer 2 around a dicing line at the end of etching of the first metal film 6 a, which will be the metallized layer 6, can be minimized.

The dry etching is performed, for example, on conditions that the gas flow ratio of BCl₃/Cl₂ is 30 sccm to 40 sccm/120 sccm to 160 sccm, the vacuum pressure is 0.7 Pa, the Mg/RF power is 600 W/50 W to 80 W, and the temperature is 25° C. Furthermore, an end point detector is preferably configured to reduce an overetching amount.

Then, the semiconductor device of FIG. 2 is completed by performing processes such as a process for thinning the buffer layer 1, for example, by polishing the back surface thereof, a process for forming the back surface electrode 9, and a process for forming the coating sealing material 8.

Overview of the First Preferred Embodiment

According to the semiconductor device according to the first preferred embodiment described above, dry etching is performed all together, and as a result the position of the first end 61 of the metallized layer 6 and the position of the second end 71 of the electrode 7 match each other in plan view. According to such a configuration, it is possible to suppress gouging or residue, which occurs in the case of wet etching. This can improve reliability of the semiconductor device. Furthermore, the influence of the gouging or residue of the first end 61 of the metallized layer 6 can be suppressed without performing patterning for each of the metallized layer 6 and the electrode 7. This can reduce a manufacturing cost.

The inventor has confirmed by simulation that an electric field intensity increases in a configuration in which there is a residue in the first end 61 of the metallized layer 6, i.e., in a configuration in which the second end 71 of the electrode 7 protrudes more toward the active region 2 a side than the first end 61 of the metallized layer 6 in plan view. Specifically, the inventor has confirmed that in a configuration in which the second end 71 is closer to the active region 2 a than the first end 61 in plan view, the electric field intensity is about twice as large as that in the configuration of the first preferred embodiment in which the position of the first end 61 and the position of the second end 71 are the same. In view of this, in the first preferred embodiment, it is possible to suppress the increase in the electric field intensity without causing a problem in an electric field distribution.

In the first preferred embodiment, the etching gas for dry etching includes BCl₃ and Cl₂. According to such a configuration, highly-controllable and uniform etching can be performed.

The inventor has confirmed by simulation that an electric field increases at an end of the p⁺ injection layer 4 a on the termination region 2 c side in the configuration in which the end of the p⁺ injection layer 4 a on the termination region 2 c side is closer to the active region 2 a than the second end 71 of the electrode 7 in plan view. On the other hand, in the first preferred embodiment, the first end 61 and the second end 71 are closer to the active region 2 a than the end of the p⁺ injection layer 4 a on the termination region 2 c side in plan view. According to such a configuration, an electric field at the end of p⁺ injection layer 4 a on the termination region 2 c side can be suppressed. It is preferable that the distance x in FIG. 2 be larger than 0 and equal to or less than 20 μm in view of the result of the simulation and from the viewpoint of a reduction of a chip invalid region (material saving and business cost reduction). That is, it is preferable that the distance x from the first end 61 and the second end 71 to the end of the p⁺ injection layer 4 a on the termination region 2 c side be larger than 0 and equal to or less than 20 μm in plan view.

The embodiments and modifications of the present invention can be freely combined and changed or omitted as appropriate within the scope of the present invention.

While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. 

What is claimed is:
 1. A method for manufacturing a semiconductor device, comprising: preparing a buffer layer having a first conductivity type; forming, on the buffer layer, a drift layer in which an active region, an interface region that surrounds the active region, and a termination region that surrounds the interface region are defined, the drift layer having the first conductivity type; forming a first impurity layer in a surface of the drift layer in the interface region, the first impurity layer having a second conductivity type; forming, in a surface of the first impurity layer, a second impurity layer that has a side and a bottom covered with the first impurity layer and has a higher impurity concentration than the first impurity layer, the second impurity layer having the second conductivity type; forming, on the first impurity layer and the second impurity layer on a termination region side, an insulating layer from which the first impurity layer and the second impurity layer on an active region side are exposed; forming a first metal film and a second metal film in this order on the insulating layer and the drift layer; and performing dry etching on the first metal film and the second metal film all together so that a position of a first end of a metallized layer, which is a remaining part of the first metal film, in the interface region on the termination region side and a position of a second end of an electrode, which is a remaining part of the second metal film, in the interface region on the terminal region side are the same in plan view, wherein the first end and the second end are closer to the active region than an end of the second impurity layer on the termination region side in plan view.
 2. The method for manufacturing the semiconductor device according to claim 1, wherein an etching gas for the dry etching includes BCl3 and Cl2. 